Geiseltalsee , literally Geisel valley lake, is at about 1,840 hectares (4,500 acres) the largest artificial lake by area in Germany. Once flooding of the Cottbuser Ostsee is complete it will surpass Geiseltalsee in surface area, covering 19 square kilometres (7.3 sq mi). Geiseltalsee lies in the Saalekreis district of the state Saxony-Anhalt . The lake was created in 2003-11 by flooding a former opencast lignite mine in the Geiseltal (Geisel valley); the name of that valley had become widely known due to the notable fossil record which emerged from that coal mine.
43-492: At 18.4 square kilometres (7.1 sq mi) surface area it is the largest artificial lake in Germany by surface area until Cottbuser Ostsee reaches its planned final size of 19 square kilometres (7.3 sq mi). Containing some 0.423 cubic kilometres (0.101 cu mi) of water it is far more voluminous than Cotbusser Ostsee will be (planned to have a volume of 0.150 cubic kilometres (0.036 cu mi) once flooding
86-548: A "rump" of 3.2 square kilometres (1.2 sq mi) surface area in winter. The lake covers what used to be the open pit lignite mine "Tagebau Cotbus Nord" which produced a total of 220 megatonnes (220,000,000 long tons; 240,000,000 short tons) of coal during its operation from 1981 to 2015. The last coal was mined in December 2015 and subsequently work began on converting the mine into a lake. Flooding started in 2019 but had to be interrupted several times due to low water levels in
129-444: A center of the chemical industry , lignite, besides being used for home heating (usually as briquettes ) and for power generation in lignite fired steam power plants , also saw extensive use as a feedstock for the chemical industry, including through processes such as coal liquefaction . While coal is less desirable as a chemical feedstock than petroleum, the ability to save on hard currency by using it to substitute petroleum made it
172-461: A depth of up to 251 metres (823 ft) and contains some 48 cubic kilometres (12 cu mi) of water. The largest reservoir (i.e. an artificial lake created via a dam) in Germany by surface area is Forggensee in Bavaria with a surface area of 15.2 square kilometres (5.9 sq mi) and a maximum water volume of 0.168 cubic kilometres (0.040 cu mi). However, this lake is reduced to
215-411: A higher shear resistance (mechanical cohesion). The shape of the grain can have an impact on the angle of repose and the stability of the slope. The more rounded the grain is, the lower the angle of repose. A decrease in roundness, or an increase in angularity, results in interlocking via particle contact. This linear relationship between the angle of repose and the roundness of grain can also be used as
258-540: A number of predisposing factors or processes that make the safety factor decrease - either by increasing the shear stress or by decreasing the shear strength - and can ultimately result in slope failure. Factors that can trigger slope failure include hydrologic events (such as intense or prolonged rainfall, rapid snowmelt, progressive soil saturation, increase of water pressure within the slope), earthquakes (including aftershocks ), internal erosion (piping), surface or toe erosion, artificial slope loading (for instance due to
301-425: A predictor of the angle of repose if the roundness of the grain is measured. Since the stability of the slope can be impacted by external events such as precipitation , an important concern in civil/ geotechnical engineering is the stabilization of slopes. The application of vegetation to increase the slope stability against erosion and landslide is a form of bioengineering that is widely used in areas where
344-477: A small stretch to the northwest. The lake is a part of the Central German Lake District . The lake is the product of extensive lignite mining in the area which first shows up in the documentary record in 1698 but which only reached significant extent in the late 19th and early 20th century when the first open-pit mines in the area were started. After World War II, the area came under the control of
387-411: A smaller surface area on which gravitational forces can act. Smaller surface area also leads to more capillary action, more water retention, more infiltration, and less runoff. The presence of vegetation does not directly impact the angle of repose, but it acts as a stabilizing factor in a hillslope , where the tree roots anchor into deeper soil layers and form a fiber‐reinforced soil composite with
430-497: A source of water to ensure quick flooding. Flooding was completed by 2011 and the water level in the new lake had risen by 1 centimetre (0.4 in) per day during flooding. A water level of 98.05 m above Normalhöhennull was reached on 29 April 2011. However, due to seapage, water from outside sources will probably have to be provided for a further two decades. Cottbuser Ostsee The Cottbuser Ostsee (Cottbus Eastern Lake; Lower Sorbian : Chóśebuski pódzajtšny jazor )
473-404: Is a static or dynamic, analytical or empirical method to evaluate the stability of slopes of soil- and rock-fill dams, embankments, excavated slopes, and natural slopes in soil and rock. It is performed to assess the safe design of a human-made or natural slopes (e.g. embankments , road cuts , open-pit mining , excavations, landfills etc.) and the equilibrium conditions. Slope stability
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#1732869442193516-447: Is an artificial lake under development on the grounds of the former open-pit lignite mine de:Tagebau Cottbus Nord near Cottbus , Brandenburg , Germany. When complete, it is to cover a surface area of 19 km (7.3 sq mi), making it one of the biggest artificial lakes in the country. At a maximum depth of 30 metres (100 ft) and an average depth of between 2.5 metres (8 ft 2 in) and 3 metres (10 ft)
559-460: Is complete) and also exceeds Germany's most voluminous reservoir , Bleilochtalsperre , by about a 2:1 margin (volume of Bleilochtalsperre being roughly 0.215 cubic kilometres (0.052 cu mi)). At a maximum depth of 78 metres (256 ft) it is the sixth deepest lake of any kind in Germany and the deepest not wholly or partly (like Lake Constance ) in the state of Bavaria. However, the depth of flooded former open pit mines tends to decrease in
602-443: Is dependent on soil properties such as grain size, which can impact infiltration rate, runoff, and water retention. Generally, finer-grained soils rich in clay and silt retain more water than coarser sandy soils. This effect is mainly due to capillary action , where the adhesive forces between the fluid, particle, and the cohesive forces of the fluid itself counteract gravitational pull. Therefore, smaller grain size results in
645-529: Is grammatically feminine, whereas "See" meaning "lake" in German is grammatically masculine. This Brandenburg location article is a stub . You can help Misplaced Pages by expanding it . This article related to a lake in Europe is a stub . You can help Misplaced Pages by expanding it . Slope stability Slope stability refers to the condition of inclined soil or rock slopes to withstand or undergo movement ;
688-424: Is locating the most-probable slip plane for any given situation. Many landslides have only been analyzed after the fact. More recently slope stability radar technology has been employed, particularly in the mining industry, to gather real-time data and assist in determining the likelihood of slope failure. Real-life failures in naturally deposited mixed soils are not necessarily circular but, prior to computers, it
731-467: Is the resistance of inclined surface to failure by sliding or collapsing. The main objectives of slope stability analysis are finding endangered areas, investigation of potential failure mechanisms, determination of the slope sensitivity to different triggering mechanisms, designing of optimal slopes with regard to safety , reliability and economics , and designing possible remedial measures, e.g. barriers and stabilization . Successful design of
774-745: The Soviet Occupation Zone which would soon give rise to the German Democratic Republic (GDR). Due to a desire for autarky and a dearth of natural resources other than lignite (and uranium in the Ore Mountains, which however mostly went to the Soviet nuclear program ), lignite mining ramped up sharply in the GDR, converting a country of less than 20 million inhabitants to the world's top producer and user of this commodity. As nearby Leuna had been
817-440: The angle of repose decreases since there is less friction between the soil grains. When the angle of repose is exceeded, mass wasting and rockfall can occur. It is important for many civil and geotechnical engineers to know the angle of repose to avoid structural and natural disasters . As a result, the application of retaining walls can help to retain soil so that the angle of repose is not exceeded. The angle of repose and
860-408: The construction of a building), slope cutting (for instance to make space for roadways, railways, or buildings), or slope flooding (for instance by filling an artificial lake after damming a river). Earthen slopes can develop a cut-spherical weakness area. The probability of this happening can be calculated in advance using a simple 2-D circular analysis package. A primary difficulty with analysis
903-470: The degree of weathering in the exposure and excavation damage. A new slope can then be designed in the ‘reference’ rock mass with compensation anticipating further damage due to excavation and future weathering. If an existing slope's stability is assessed, the ‘exposure’ and ‘slope’ rock mass values are the same. The failure mechanisms are divided into orientation dependent and orientation independent . Orientation dependent failure mechanisms depend on
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#1732869442193946-431: The destabilizing forces. Once the slip has occurred, however, a weakness along the slip circle remains, which may then recur at the next monsoon. The angle of repose is related to the shear strength of geologic materials, which is relevant in construction and engineering contexts. For granular materials, the size and shape of grains can impact angle of repose significantly. As the roundness of materials increases,
989-455: The first few decades after flooding, as evidenced by Senftenberger See which was flooded from 1967 to 1972 reaching a maximum depth of 40 metres (130 ft) but which has no point exceeding a depth of 25 metres (82 ft) according to more recent measurements. Geiseltalsee is bordered by the village of Mücheln to the southwest, west, and northwest, the towns of Braunsbedra to the northeast, east, and southeast, and of Bad Lauchstädt for
1032-405: The former pit. Besides allowing quick conversion to new uses, quick flooding is also desirable as it reduces the risk and amount of acid mine drainage (minerals like pyrite which are stable in anoxic conditions oxidize if exposed to air, giving rise to sulfuric acid - this process is slowed or stopped by covering those minerals in water). Thus it was decided to use the nearby Saale river as
1075-406: The initiation of such movement, slowing it down or arresting it through mitigation countermeasures. The stability of a slope is essentially controlled by the ratio between the available shear strength and the acting shear stress , which can be expressed in terms of a safety factor if these quantities are integrated over a potential (or actual) sliding surface. A slope can be globally stable if
1118-558: The lake is to have a total water volume of 0.150 cubic kilometres (0.036 cu mi) once flooding is complete. Until the lake is complete, the biggest artificial lake in Germany by surface area (likewise created by conversion of a former lignite mine) is Geiseltalsee which covers some 1,840 hectares (4,500 acres). However, the water volume of Geiseltalsee is almost three times larger at 0.423 cubic kilometres (0.101 cu mi). For comparison, Germany's largest lake, Lake Constance , covers 536 square kilometres (207 sq mi) at
1161-502: The landslide depth is shallow. Vegetation increases the stability of the slope mechanically, by reinforcing the soils through plant roots, which stabilize the upper part of the soil. Vegetation also stabilizes the slope via hydrologic processes, by the reduction of soil moisture content through the interception of precipitation and transpiration . This results in a drier soil that is less susceptible to mass wasting. Stability of slopes can also be improved by: Slope stability analysis
1204-406: The materials that make up the pit slope will reduce the strength of those materials. Choice of correct analysis technique depends on both site conditions and the potential mode of failure, with careful consideration being given to the varying strengths , weaknesses and limitations inherent in each methodology . Various classification and rating systems exist for the design of slopes and to assess
1247-403: The mine closed on 30 June 1993 exactly a decade of earthworks to ensure slope stability and eliminate the danger of landslides followed and flooding started on 30 June 2003. While all open pit mines operating below the natural water table require the lowering of the water table (usually via extensive pumping), simply letting the water table rise naturally is usually not enough to quickly flood
1290-622: The nearby Spree River . The lake is to become part of the Lusatian Lake District , a chain of artificial lakes mostly the result of open-pit lignite mining. The name - besides referring to the location of the lake to the East of central Cottbus - can be interpreted as a pun on the German name for the Baltic Sea , which is called "Ostsee" in German, the two words only being distinguished by their grammatical gender : "See" meaning "sea" in German
1333-419: The opposite condition is called slope instability or slope failure . The stability condition of slopes is a subject of study and research in soil mechanics , geotechnical engineering , and engineering geology . Analyses are generally aimed at understanding the causes of an occurred slope failure, or the factors that can potentially trigger a slope movement, resulting in a landslide , as well as at preventing
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1376-421: The orientation of the slope to the discontinuities in the rock mass, i.e., sliding (plane and wedge sliding) and toppling failure. Orientation independence relates to the possibility that a slope fails independently from its orientation, e.g., circular failure entirely through newly formed discontinuities in intact rock blocks or failing partially following existing and partially new discontinuities. In addition,
1419-685: The preferred solution in East Germany. After German reunification, the demand for lignite dropped sharply as reunified Germany could import petroleum on the world market and superior domestic hard coal from the Ruhr area and other then-active mining areas in West Germany competed with lignite. Furthermore, lignite is by far the most ecologically damaging fossil fuel due to its high moisture content, high sulfur content (producing acid rain upon combustion) and frequent contamination with toxic heavy metals . Thus it
1462-400: The resulting "holes" left over from mining (even if all overburden were filled back into the former mine, the "missing" coal would mean the surface would still be below the natural water table ) as had been done with what is now Senftenberger See , the plans for the 80 metres (260 ft) deep and 2,600 hectares (6,400 acres) wide former mine were only seriously made after reunification. After
1505-408: The safety factor, computed along any potential sliding surface running from the top of the slope to its toe, is always larger than 1. The smallest value of the safety factor will be taken as representing the global stability condition of the slope. Similarly, a slope can be locally stable if a safety factor larger than 1 is computed along any potential sliding surface running through a limited portion of
1548-420: The slope (for instance only within its toe). Values of the global or local safety factors close to 1 (typically comprised between 1 and 1.3, depending on regulations) indicate marginally stable slopes that require attention, monitoring and/or an engineering intervention ( slope stabilization ) to increase the safety factor and reduce the probability of a slope movement. A previously stable slope can be affected by
1591-438: The slope requires geological information and site characteristics, e.g. properties of soil / rock mass, slope geometry , groundwater conditions, alternation of materials by faulting , joint or discontinuity systems, movements and tension in joints, earthquake activity etc. The presence of water has a detrimental effect on slope stability. Water pressure acting in the pore spaces, fractures or other discontinuities in
1634-433: The stability of a slope are impacted by climatic and non-climatic factors. Water content is an important parameter that could change the angle of repose. Reportedly, a higher water content can stabilize a slope and increase the angle of repose. However, water saturation can result in a decrease in the slope's stability since it acts as a lubricant and creates a detachment where mass wasting can occur. Water content
1677-460: The stability of slopes. The systems are based on empirical relations between rock mass parameters and various slope parameters such as height and slope dip. The slope stability probability classification (SSPC) system is a rock mass classification system for slope engineering and slope stability assessment. The system is a three-step classification: ‘exposure’ , ‘reference’ , and ‘slope’ rock mass classification with conversion factors between
1720-413: The three steps depending on existing and future weathering and depending on the damage incurred by excavation. The stability of a slope is expressed as the probability of different failure mechanisms. A rock mass is classified following a standardized set of criteria in one or more exposures ( ‘exposure’ classification). These values are converted per exposure to a ‘reference’ rock mass, compensating for
1763-481: The top of the slip may also fill with rain water, pushing the slip forward. At the other extreme, slab-shaped slips on hillsides can remove a layer of soil from the top of the underlying bedrock. Again, this is usually initiated by heavy rain, sometimes combined with increased loading from new buildings or removal of support at the toe (resulting from road widening or other construction work). Stability can thus be significantly improved by installing drainage paths to reduce
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1806-431: Was decided to wind down large parts of East German lignite mining with the mines now covered by the lake shut down in 1993. By that point some 1.4 gigatonnes (1.4 × 10 long tons; 1.5 × 10 short tons) of lignite and a similar amount of overburden had been mined over the existence of the mine and some 12,500 people who had lived on land now taken up by mining had had to be resettled. While there had been vague plans to flood
1849-475: Was far easier to analyze such a simplified geometry. Nevertheless, failures in 'pure' clay can be quite close to circular. Such slips often occur after a period of heavy rain, when the pore water pressure at the slip surface increases, reducing the effective normal stress and thus diminishing the restraining friction along the slip line. This is combined with increased soil weight due to the added groundwater. A 'shrinkage' crack (formed during prior dry weather) at
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